Nuclear reactors are used to generate power (e.g., electrical power) using nuclear fuel materials. For example, heat generated by nuclear reactions carried out within the nuclear fuel materials may be used to boil water, and the steam resulting from the boiling water may be used to rotate a turbine. Rotation of the turbine may be used to operate a generator for generating electrical power.
Nuclear reactors generally include what is referred to as a “nuclear core,” which is the portion of the nuclear reactor that includes the nuclear fuel material and is used to generate heat from the nuclear reactions of the nuclear fuel material. The nuclear core may include a plurality of fuel rods, which include the nuclear fuel material.
Most nuclear fuel materials include one or more of the elements of uranium and plutonium (although other elements such as thorium are also being investigated). There are, however, different types or forms of nuclear fuel materials that include such elements. For example, nuclear fuel pellets may comprise ceramic nuclear fuel materials. Ceramic nuclear fuel materials include, among others, radioactive uranium oxide (e.g., uranium dioxide, UO2, which is often abbreviated as “UOX”), which is often used to form nuclear fuel pellets. Mixed oxide radioactive ceramic materials (which are often abbreviated as “MOX”) are also commonly used to form nuclear fuel pellets. Such mixed oxide radioactive ceramic materials may include, for example, a blend of plutonium oxide and uranium oxide. Such a mixed oxide may include, for example, U1-xPuxO2, wherein x is between about 0.2 and about 0.3. Transuranic (TRU) mixed oxide radioactive ceramic materials (which are often abbreviated as “TRU-MOX”) also may be used to form nuclear fuel pellets. Transuranic mixed oxide radioactive ceramic materials include relatively higher concentrations of minor actinides such as, for example, neptunium (Np), americium (Am), and curium (Cm). Carbide nuclear fuels and mixed carbide nuclear fuels having compositions similar to the oxides mentioned above, but wherein carbon is substituted for oxygen, are also being investigated for use in nuclear reactors.
In addition to ceramic nuclear fuel materials, there are also metallic nuclear fuel materials. Metallic nuclear fuels include, for example, metals based on one or more of uranium, plutonium, and thorium. Other elements such as hydrogen (H), zirconium (Zr), molybdenum (Mo), and others may be incorporated into uranium- and plutonium-based metals.
In nuclear reactors that employ metallic nuclear fuels, the metallic nuclear fuel is often formed into rods or pellets of predetermined size and shape (e.g., spherical, cubical, cylindrical, etc.) that are at least substantially comprised of the metallic nuclear fuel. The nuclear fuel material is contained within and at least partially surrounded by a cladding material, which may comprise, for example, an elongated tube. The cladding material is used to hold and contain the nuclear fuel. The cladding material typically comprises a metal or metallic alloy, such as stainless steel. During operation of the nuclear reactor, the cladding material may separate (e.g., isolate and hermetically seal) the nuclear fuel bodies from a liquid (e.g., water or molten salt) that is used to absorb and transport the heat generated by the nuclear reaction occurring within the nuclear fuel.
Zirconium-based metal alloys have been employed as cladding materials, since they may exhibit relatively low absorption of thermal neutrons. For example, a class of such zirconium-based metal alloys is referred to in the art as “Zircaloys.” Another zirconium-based alloy that has been employed as cladding material is referred to in the art as “M5” alloy. M5 alloy has been reported to contain, in weight percentages: niobium 0.81-1.2 wt %; oxygen 0.090-0.149 wt %, zirconium—the balance (Mardon et al., Update on the Development of Advanced Zirconium Alloys for PWR Fuel Rod Claddings, International Topical Meeting on Light Water Reactor Fuel Performance, Portland, Oreg. (Mar. 2-6, 1997) (Published by the American Nuclear Society, Inc., La Grange Park, Ill. 60526, USA). It is known that Zircaloys and M5 Alloy have a relatively affinity to hydrogen. Absorption of hydrogen in Zircaloys and M5 Alloy may lead to hydrogen embrittlement. When such alloys are employed as cladding material in nuclear fuel bodies and reactors, such hydrogen embrittlement can lead to failure of the cladding material.